The present invention relates to a device for lighting a liquid crystal display device employed, for example, in a television, and more particularly to a back-lighting device for the liquid crystal display device. It is required to light the lighting device at uniform luminance.
Such lighting devices are disclosed in Japanese Utility Model Applications, Laid-open Nos. 53-13166 and 62-27329.
In the application of No. 53-13166, a reflector of a lighting device is provided under a liquid crystal display panel. The reflector has a plurality of flat surface portions and a plurality of uneven or rough surface portions which are combined to form a surface of a striped, checkered, or spotted pattern. A lamp is provided above the reflector, and the light from the lamp is reflected on the flat surface portions in total reflection and on the uneven surface portions in diffuse reflection, so that the display panel is uniformly lighted.
In the application of No. 62-27329, a lighting device is provided under a liquid crystal display panel, interposing a diffusion sheet. The lighting device comprises a pair of parabolic mirrors with rough surfaces and a pair of fluorescent lamps mounted above the corresponding mirrors. Thus, the light from the lamps which are provided between the mirrors and the diffusion sheet is reflected in diffuse reflection for uniformly lighting the display panel.
However, there are disadvantages in the prior art disclosures as follows. In the former device, since the reflector is formed in flat and the lamp is provided at the outside of the reflector, the light from the lamp does not reach sufficiently to portions of the display panel apart from the lamp, so that the entire surface of the panel cannot be uniformly lighted.
In the latter device, it is necessary to provide a sufficient distance between the diffusion sheet and parabolic mirrors for preventing the diffusion sheet from abnormally brightening at portions adjacent the lamps. If a sufficient distance is provided, the luminance of the diffusion sheet as a whole decreases to deteriorate lighting efficiency. Further, the disposition of the large space causes an increase in size and thickness of the display device.
In order to eliminate these defects, the parabolic mirror of the latter device may be substituted with a parabolic mirror having a total reflection surface. However, since the luminance characteristics are dependent on the shape of the reflector, manufacturing the reflector is complicated requiring many steps. Further, since light reflects on the total reflection surface at an angle of reflection equal to an angle of incidence, the light is liable to aggregate at opposite side portions of the display panel.